Elastic sealing material on the basis of block copolymers made of isobutene and vinyl aromatic monomers

ABSTRACT

Linear or star block copolymers which have at least one polymer block A which is essentially composed of isobutene units and at least two polymer blocks B which are essentially composed of units which are derived from vinylaromatic monomers are used as resilient sealing material. In particular, such sealing materials are used for sealing the edge joints in insulation glass panes, and insulation glass panes have a flexible edge joint seal which contains one of the block copolymers.

The present invention relates to the use of block copolymers comprisingpolymer blocks A which are essentially composed of isobutene and polymerblocks B which are essentially composed of units which-are derived fromvinylaromatic monomers, as resilient sealing materials.

Flexible sealing materials, also referred to as sealing compounds, areused, for example, for sealing joints. Typical sealing compounds consistof polysulfide, butyl rubber, silicones or resilient polyurethanes.Depending on the use, the sealing materials must fulfill stringentrequirements. They may not lose their resilience under extremetemperature variations and may not become brittle, especially at lowtemperatures. At the same time, high mechanical strength is oftendesired. Furthermore, the sealing materials should be stable to theeffects of weathering and/or to chemicals, for example to householdcleaners. For a number of applications, in particular extremely low gaspermeability, in particular to air, argon and water vapor, is required.

For example, sealing materials having high resilience and mechanicalstrength in combination with low gas permeability are required for theproduction of insulation glass windows. Insulation glass windows consistas a rule of two or more glass panes which are kept apart by spacers,for example by aluminum rails or hollow aluminum profiles. The spacebetween the individual glass panes is as a rule filled with a gas, forexample argon or sulfur hexafluoride, for better insulation. The jointsbetween the individual glass panes, in particular the joints between thealuminum profiles and the glass panes, must be sealed with a sealingmaterial which, on the one hand, prevents the escape of the insulatinggas and, on the other hand, prevents penetration of atmospherichumidity, i.e. air and water vapor, into the space between the glasspanes.

The prior art solves the problem by adhesively bonding the aluminumprofiles acting as spacers to the glass panes by means of a layer ofpolyisobutene which simultaneously acts as a sealing compound. In thisway, high gastightness is achieved. However, this type of seal does notresult in sufficient mechanical strength of the composite pane and issensitive to mechanical damage. In the prior art, this structure istherefore covered with a further sealing compound having highermechanical strength. For example, cold-crosslinkable orhot-crosslinkable sealing materials comprising polysulfide, butylrubber, silicones or polyurethanes are suitable for this purpose. Theuse of two sealing materials makes the application of such seals moreexpensive and thus increases the production costs for insulationglazing. In addition, such sealing materials have only insufficient gasimpermeability.

It is an object of the present invention to provide a flexible sealingmaterial which is impermeable to gases such as argon or water vapor andat the same time has high resilience in combination with sufficientmechanical strength.

We have found that this object is achieved and that, surprisingly, theserequirements set for sealing materials are fulfilled by block copolymerswhich contain at least one polymer block A which is composed ofisobutene units and at least two further polymer blocks B which arecomposed of units which are derived from vinylaromatic monomers.

The present invention accordingly relates to the use of linear or starblock copolymers which have at least one polymer block A which isessentially composed of isobutene units and at least two polymer blocksB which are essentially composed of units which are derived fromvinylaromatic monomers, as resilient sealing material.

Block copolymers based on isobutene and vinylaromatic monomers andprocesses for their preparation are known from the prior art (cf. forexample U.S. Pat. No. 4,946,899 and literature stated therein).

Both linear block copolymers, for example of the type B-A-B or(A-B-)_(k)A, where k≧2, and star block copolymers are suitable for theuse according to the invention. Among these, those block copolymerswhich have a central polymer block which is essentially composed ofisobutene units are preferred. Such block copolymers having a centralpolyisobutene block are of the formula I

where

A is a polymer block A according to the above definition,

B is a polymer block B according to the above definition,

n is 0, 1 or 2 and

X is a single bond or an n+2-valent hydrocarbon radical of up to 30carbon atoms.

If X is an n+2-valent hydrocarbon radical, this is a consequence of thepreparation and results from the respective polymerization initiator.Together with the polymers blocks A surrounding it, it forms the centralpolymer block which is essentially composed of isobutene units.

According to the invention, the block copolymer contains at least onepolymer block A which is essentially composed of isobutene units. Someof the isobutene units in the polymer blocks may also be replaced bymonoolefinically unsaturated monomers having silyl groups. Typical silylgroups are trialkoxysilyl groups in which the alkoxy radical has, as arule, 1, 2, 3 or 4 carbon atoms and may in turn be substituted byC₁-C₄-alkoxy. Examples of such radicals are trimethoxysilyl,triethoxysilyl, tri-n-propoxysilyl and tri(methoxyethyl)silyl. Thepolymer blocks A then preferably contain up to 20, for example from 0.1to 20, in particular from 0.5 to 10, % by weight, based on the totalweight of all polymer blocks A in the block copolymer, of such monomersas polymerized units. Examples of monoolefinically unsaturated monomershaving trialkoxysilyl groups are in particular C₂-C₁₀-monoolefins whichare substituted by a tri-C₁-C₄-alkoxysilyl group: these includetrialkoxysilyl-substituted ethene, propene, n-butene, isobutene,n-pentene, 2-methyl-1-butene or 2-methyl-1-pentene. Examples of suchmonomers are: 1-(trimethoxysilyl)ethene, 1-(trimethoxysilyl)propene,1-(trimethylsilyl)-2-methyl-2-propene,1-(tri(methoxyethoxy)silyl)ethene, 1-(tri(methoxyethoxy)silyl)propene,1-(tri(methoxyethoxy)silyl)-2-methyl-2-propene. Styrene derivativeswhich have one of the abovementioned trialkoxysilyl groups, for example2-, 3- or 4-trimethoxysilylstyrene, or compounds of the typeCH₂═CH—C₆H₄—Q—Si(OCH₃)₃, where Q is a bifunctional radical, for examplea C₁-C₁₀-alkylene group, which may be interrupted by one or more,nonneighboring oxygen atoms or imino groups, e.g. —CH₂—NH—C₂H₄—NH—C₃H₆—,are also suitable. Such monomers derived from styrene may also be usedfor modifying the styrene block.

According to the invention, the block copolymer contains at least onefurther polymer block B which is composed of units which are derivedfrom vinylaromatic monomers. Suitable vinylaromatic monomers are:styrene, α-methylstyrene, C₁-C₄-alkylstyrenes, such as 2-, 3- and4-methylstyrene and 4-tert-butylstyrene, and 2-, 3- or 4-chlorostyrene.Preferred vinylaromatic monomers are styrene and 4-methylstyrene andmixtures thereof. A very particularly preferred vinylaromatic monomer isstyrene, which may be replaced by up to 20% by weight of4-methylstyrene.

In the formula II, X is preferably a 2- or 3-valent hydrocarbon radicalof up to 30, preferably 5 to 20, carbon atoms. X links the polymerblocks A surrounding it and composed of isobutene to a central polymerblock which is essentially composed of isobutene units. X is preferablyone of the following radicals:

where m is 1, 2 or 3

The number-average molecular weight of the central polyisobutene blockcorresponds approximately to the sum of the number-average molecularweights of all polymer blocks A in formula I. This is as a rule from20,000 to 100,000, preferably from 25,000 to 90,000, very particularlypreferably from 30,000 to 80,000 daltons. The ratio of the total weightof all polymer blocks A to the total weight of all polymer blocks B isas a rule from 1:1 to 9:1, preferably from 1.2:1 to 4:1, in particularfrom 3:2 to 7:3.

In the interest of mechanical strength, it has proven advantageous ifthe polymer block or polymer blocks B which is or are composed ofvinylaromatic monomers has or have a number-average molecular weightM_(n) of at least 6000, in particular from 7000 to 20,000, daltons.

It has also proven advantageous if the polymer block or polymer blocks Ahas or have a narrow molecular weight distribution. The width of themolecular weight distribution can be characterized on the basis of thedispersity (ratio of weight-average molecular weight to number-averagemolecular weight M_(w)/M_(n)). The dispersity M_(w)/M_(n) is preferablyless than 1.4, in particular less than 1.3, particularly preferably lessthan 1.2.

All molecular weight data relate to values as determined by means of gelpermeation chromatography (GPC). The gel permeation chromatography wascarried out using THF as a mobile phase and CS₂ as reference, on twocolumns (length 300 mm, diameter 7.8 mm) connected in series, the firstcolumn being packed with Styragel HR5 (molecular weight range from50,000 to 4×10⁶) and the second column with Styragel HR3 (molecularweight range from 200 to 30,000) from Waters. The detection was carriedout by means of a differential refractometer. Commercial polyisobutenestandards in the molar mass range from 224 to 1,000,000, fromPolymer-Standards Service, Mainz, Germany, were used as standards fordetermining the isobutene block. In the determination of the blockcopolymers, a polystyrene calibration file and a UV detector wereadditionally used.

The block copolymers used according to the invention can be prepared bythe processes customary for the preparation of block copolymers. In afirst process, a first polymer block which is essentially composed ofisobutene units and which carries functional groups at its end isprepared by known processes, for example cationically initiatedpolymerization, and these functional groups are used as a starting pointfor the polymerization of the vinylaromatic monomers or as a linkagepoint to prepared blocks of vinylaromatic monomers which in turn carryfunctional groups on the terminal groups. For example, polymer blockscomprising isobutene units which carry halogen, e.g. chlorine, as afunctional group at their end can be prepared by known processes. Thesehalogen atoms can be metalated by known processes, for example byreaction with organometallic reagents, such as butyllithium, and serveas a starting point for an anionic polymerization of the vinylaromaticmonomers.

In another preparation process, a polymer block which has functionalgroups which can be converted into cationic centers by Brönsted or Lewisacids is first prepared. The center then serves as a starting point forthe cationically initiated polymerization of vinylaromatic monomers orof isobutene. Processes for this purpose are known in principle (cf. forexample J. P. Kennedy et al. “Designed Polymers by CarbocationicMacromolecular Engineering”, Carl Hanser-Verlag, Munich, Vienna, NewYork, Barcelona, pages 197 to 220). Polyisobutenes having functionalterminal groups, for example with halogen, can be prepared, for example,by cationic polymerization of isobutenes. Processes for this purpose arelikewise described in the prior art (cf. for example J. P. Kennedy etal., loc. cit. pages 167 to 195).

The block copolymers used according to the invention can moreover beprepared in a simple manner by sequential, cationically initiatedpolymerization, isobutene or a monomer mixture which essentiallycomprises isobutene first being polymerized under the conditions of aliving cationic polymerization, and polymerization of the vinylaromaticmonomers then being carried out under these conditions. Such apolymerization sequence is known in principle and was described, forexample, by J. P. Kennedy et al. in U.S. Pat. No. 4,946,899 and Fodor etal. in J. Macromol. Sci.-Chem., A24 7 (1987), pages 735 to 747. Forfurther details, the content of these publications is herebyincorporated in their entirety by reference.

In this process, isobutene is first reacted in the presence of acoinitiator, of a Lewis acid and, if required, of a compound having afree electron pair, under aprotic conditions.

In the simplest case, suitable coinitiators are monofunctional compoundsof the formula R—Y, where R is a hydrocarbon radical and Y is a leavinggroup which can be activated by a Lewis acid. The presence of the Lewisacid results in elimination of the leaving group with formation of apositive charge or of positive polarization of the carbon atom in R towhich the leaving group Y is bonded.

Examples of typical leaving groups are halogens, such as chlorine,bromine or iodine, in particular chlorine, linear or branchedC₁-C₆-alkoxy groups, such as methoxy, ethoxy, n-propoxy, isopropoxy,n-butoxy, isobutoxy, sec-butoxy or tert-butoxy, and linear or branchedC₁-C₆-acyloxy groups, such as acetoxy, propionyloxy, n-butyroxy,isobutyroxy, n-butylcarbonyloxy, isobutylcarbonyloxy orsec-butylcarbonyloxy or pivalyloxy. The leaving group Y is bonded to acarbon atom in the radical R which is capable of forming a stablecarbocation or at least stabilizing a positive partial charge.Preferably, Y is therefore bonded to a secondary or in particular to atertiary carbon atom. In particular, the carbon atom to which Y isbonded carries two methyl groups. The carbon atom to which Y is bondedpreferably carries a group which is capable of stabilizing a cationiccharge by mesomerism, for example a vinyl group or a phenyl group.Typical radicals R are n-butyl, isobutyl, sec-butyl, tert-butyl,2,4-dimethylpent-2-yl, 2-vinylprop-2-yl and radicals which are derivedfrom lower oligomers of isobutene and are of the formula

where 1 is 3, 4 or 5.

For the preparation of the block copolymers preferred according to theinvention and having a central polymer block which is essentiallycomposed of isobutene units, compounds which contain at least twofunctional leaving groups are used as coinitiators, i.e. compounds ofthe formula II

where X and n have the meanings stated above in connection with formulaI and Y is a leaving group, preferably a leaving group stated inconnection with R—Y. Here too, Y is preferably halogen, C₁-C₆-alkoxy orC₁-C₆-acyloxy, in particular chlorine, bromine, methoxy or acetoxy,chlorine being particularly preferred. Here too, Y is preferably bondedto a tertiary carbon atom. The tertiary carbon atom preferably has atleast one methyl group and in particular two methyl groups. Preferably,this carbon atom carries a group which is capable of stabilizing acationic charge by resonance, for example a vinyl or phenyl group.Examples of particularly preferred coinitiators are the compoundsmentioned below:

where m is 1, 2 or 3

where Y may be identical or different and have one of the abovementionedmeanings. In these formulae, too, Y is preferably chlorine, bromine,methoxy or acetoxy, in particular chlorine.

The Lewis acids used for the preparation are as a rule compounds such asaluminum halides, titanium(IV) halides, boron halides, tin(IV) halidesor zinc halides, in particular the chlorides. The abovementioned halidesmay also have an alkyl substituent instead of some of the halogen atoms.Examples of these are the mono- and dialkyl halides of boron and ofaluminum, in particular the mono- and dialkyl chlorides. In thepreparation to give higher molecular weights, pentafluorophenylcompounds of the above-mentioned elements, in particulartris(pentafluorophenyl)borane, have also proven useful. Particularlypreferred Lewis acids are titanium tetrachloride and boron trichloride,in particular titanium tetrachloride. In the preparation of the novelblock copolymers, in particular in the polymerization of the isobuteneblock, the molar ratio of coinitiator to Lewis acid is from 2:1 to 1:50,preferably from 1:1 to 1:20, in particular from 1:2 to 1:10, based onthe functional groups in the coinitiator.

It is known that the molecular weight of the polymer block firstpolymerized, which is composed of isobutene units, can be established bymeans of the ratio of isobutene to coinitiator. As a rule, theisobutene/coinitiator ratio is from 10,000:1 to 100:1, preferably from5000:1 to 500:1.

In the preparation of the novel block copolymers by cationicpolymerization, it has proven advantageous if a further, nonacidiccompound having a free electron pair is added as a further cocatalyst tothe polymerization mixture. Such compounds presumably form complexeswith the Lewis acid under the polymerization conditions and thusregulate their reactivity. Examples of such compounds are dialkylethers, such as diisopropyl ether, cyclic ethers, such astetrahydrofuran, trialkylamines such as triethylamine ordiisopropylamine, amides, such as N,N-dimethylacetamide, C₁-C₄-alkylesters of aliphatic C₁-C₆-carboxylic acids, such as ethyl acetate,dialkyl thioethers or alkylaryl thioethers, such as methyl phenylsulfide, dialkyl sulfoxides, such as dimethyl sulfoxide, nitriles, suchas acetonitrile, trialkylphosphines or triarylphosphines, such astrimethylphosphine, triethylphosphine, tri-n-butylphosphine andtriphenylphosphine, pyridine or alkylpyridines. Particularly preferredamong these are pyridine and sterically hindered pyridine derivatives.Sterically hindered pyridines are those which have sterically bulkyalkyl groups at least in the 2- and 6-position of the pyridine ring,e.g. 2,6-diisopropylpyridine and 2,6-di-tert-butylpyridine. Stericallyhindered pyridine derivatives presumably serve as proton traps and thusprevent protons from ubiquitous traces of water from initiating afurther cationic polymerization.

A a rule, the cationic polymerization for the preparation of the novelblock copolymers is carried out in a solvent. Suitable solvents arethose which are still liquid under the usually low reaction temperaturesand neither eliminate protons nor have free electron pairs. Examples ofthese are cyclic and acyclic alkanes, such as ethane, isopropane,n-propane, n-butane, isobutane, n-pentane and isomers of pentane,cyclopentane, n-hexane and hexane isomers, n-heptane and heptane isomersand alkyl-substituted cyclohexanes. Mixtures of these nonpolar solventswith halogenated hydrocarbons, such as methyl chloride, dichloromethane,ethyl chloride, dichloroethanes and neopentyl chlorides, are preferablyused. This makes it possible to adjust the polarity of the solvent inthe desired manner. A higher polarity of the solvent generally resultsin a higher reaction rate. Conversely, the solubility of the polymersimproves with a reduction in the polarity. Moreover, a lower solventpolarity results in a lower transfer probability and hence highuniformity of the polymer.

Before they are used in the living cationic polymerization, the startingmaterials, i.e. the monomers and the solvents, are subject topurification and drying. Sufficient drying of the monomers and of thesolvents can be effected, for example, by treatment with dry molecularsieves or anhydrous alumina. The monomers are preferably dried overmolecular sieves 3A and/or alumina at below 200° C. The solvents are asa rule subjected beforehand to preliminary purification over ionexchangers or by washing with sulfuric acid or with sodium hydroxidesolution.

For the preparation of the block copolymers of the formula II, as a ruleisobutene or monomer mixtures essentially containing |isobutene arefirst reacted in one of the abovementioned solvents in the presence ofthe abovementioned coinitiators and Lewis acids at below 0° C.,preferably from −20 to −120° C., in particular from −50 to −100° C.,until the desired conversion of the isobutene has been reached. Thevinylaromatic monomers are then added for producing the polymer blocksB. During or after the addition of the vinylaromatic monomers, thereaction temperature can be maintained or, depending on the reactivityof the vinylaromatic monomers, increased. In this case, thepolymerization of the vinylaromatic monomers is carried out at above−50° C., for example at from −20 to +50° C. As a rule, thepolymerization of the isobutene is continued to a conversion of at least80%, preferably at least 90%, before the vinylaromatic monomers areadded. The vinylaromatic monomers are preferably added before 99%, inparticular before 98%, of the isobutene has been converted, sinceotherwise there is the danger that some of the reactive terminal groupswill be deactivated. As a result of this procedure, a central polymerblock essentially composed of isobutene units (or a plurality of polymerblocks A which are arranged around the radical X) first forms, saidpolymer block carrying at its ends polymer blocks B which are composedof vinylaromatic monomers and are essentially unsegmented, i.e. free ofisobutene units.

The reaction can be carried out batchwise or semicontinuously(semibatch, feed process). However, the preparation is preferablycarried out batchwise in conventional stirred kettles. At least some,preferably the total amount of, isobutene and solvent is preferablyinitially taken in the reaction vessel. Thereafter, the coinitiator and,if required, the cocatalyst in the Lewis acid, preferably in this order,are first added at the desired polymerization temperature and theisobutene polymerization is carried out with cooling to the desiredconversion. The vinylaromatic monomers are then added and if necessarythe polymerization temperature is increased.

The heat of reaction can be removed in the usual manner, for example byinternal or external cooling units and/or evaporative cooling.

Workup can be effected in a conventional manner, first the Lewis acidbeing decomposed with water or with alcohols, e.g. isopropanol, andworkup then being effected in an aqueous medium by extraction. It hasproven advantageous if, after the reaction has been stopped, the solventor solvent mixture used for the reaction is first replaced by anaromatic hydrocarbon in order to achieve a clear phase separation. As arule, the organic phase or the crude product isolated therefrom issubjected to an aftertreatment with dry alumina, water, halogens, suchas chloride, organic halogen compounds and tert-butanol being removed.

The block copolymer obtainable according to the invention can be useddirectly as sealing material or can be compounded with the conventionaladditives. The novel block copolymers, in particular the block copolymesof the formula I, are distinguished by high water vapor and gastightness which, in spite of the polystyrene blocks, is comparable withthat of isobutene. The novel block copolymers are extremely resilientand, in contrast to isobutene, have substantially higher tensilestrength and a substantially higher surface hardness. Furthermore, theblock copolymers exhibit thermoplastic behavior, which permits simpleprocessing, for example by melt extrusion.

Investigation of the novel block copolymers by means of DSC(differential scanning calorimetry) shows a narrow, glassy transitionabove 90° C., which indicates substantially unsegmented polymer blocksB.

Owing to these properties, the novel block copolymers are particularlysuitable for the production of resilient sealing materials or sealingcompounds for a large number of applications.

The novel block copolymers can be used as such as sealing materials.However, depending on the application, the novel sealing materials canbe used for the preparation of sealing compounds which, in addition tothe novel sealing materials, contain conventional additives, for exampleUV stabilizers and processing assistants and/or fillers in the amountscustomary for sealing compounds. In particular, such sealing compoundsbased on the novel sealing material may contain up to 40, preferably upto 20, % by weight of conventional fillers, e.g. carbon blacks, metalpowder, inorganic or organic pigments and other fillers. Suitableadditives and fillers are known to a person skilled in the art. Theseare fillers as usually used in sealing compounds based on siliconerubbers, butyl rubbers or polysulfide.

Owing to their property profile, the novel flexible sealing material orsealing compounds prepared therefrom are particularly suitable forsealing the edge joints of insulation glass panes. Accordingly, thepresent invention also relates to the use of the novel block copolymersin sealing compounds for sealing edge joints in insulation glass panes.It also relates to insulation glass panes having an edge joint sealwhich contains, as flexible sealing material, one of the blockcopolymers described above. Insulation glass panes which are providedwith such edge joint seals are distinguished by a longer life, inparticular with respect to the undesired penetration of traces ofmoisture into the spaces present between the glass panes.

In FIG. 1, an insulation glass pane is illustrated by way of example. Inthe arrangement shown, the insulation glass pane has, as a spacer, ahollow aluminum profile which is arranged between two glass panes (1)and connected to the glass panes (1) by an adhesive bond (3). Theadhesive bond (3) can be effected by means of a polyisobutene of theprior art or by means of a novel block copolymer. The hollow aluminumprofile (2) may contain a drying agent (4). In this case, the hollowprofile (2) has orifices (5), for example in the form of holes or slots,in the surfaces, which openings form the boundary with the cavitypresent between the glass panes. Furthermore, such insulation glasspanes have a flexible covering (6) of the edge joints formed from thehollow profile (2) and the panes (1). The novel sealing materials areused as material for the covering (6) of the edge joints.

The composite panes thus obtained are distinguished by improvedmechanical stability and greater stability to the penetration ofatmospheric humidity into the space between the panes.

Owing to the particular property profile of the novel sealing materials,i.e. their low gas permeability and their high mechanical strength, theexpensive hollow aluminum profile can be dispensed with. Accordingly, afurther novel embodiment relates to those insulation glass panes whichhave any desired spacer, for example of plastics, instead of the hollowaluminum profile. This spacer is embedded directly in the edge jointseal comprising the novel sealing materials. An adhesive bond with theglass pane can be dispensed with. Consequently, the traditionalarrangement comprising a hollow aluminum profile as a spacer issimplified. Moreover, the omission of the hollow aluminum profile leadsto improve heat insulation of the panes. Owing to the high water vaporpermeability, it has to date been impossible to dispense with a hollowaluminum profile when conventional sealing materials are used as edgejoint seals.

EXAMPLES 1. Analysis

The molecular weight was determined by means of GPC againstpolyisobutene standard and against a polystyrene calibration file in themanner described above.

Determination of the solution viscosity: for this purpose, the viscositywas determined according to Ubbelohde (capillary diameter 0.01 mm) at20° C. in isooctane (1 g of polymer in 100 ml) according to DIN 51562.

Determination of the mechanical properties:

a) Hardness test: the Shore A hardness (DIN 53505) was determined.

b) In the tensile test according to DIN 53504, the tensile strength omaxand the maximum extensibility ε-F_(max) were determined on 1.04 mm thickand 4 mm wide test specimens.

The water vapor permeability was determined according to ASTM F-1249 andthe permeability to argon according to DIN 53380, using films having athickness of 237 μm.

2. Preparation of the Novel Block Copolymers (Example 1)

Two dropping funnels having a capacity of 1 l each are placed on a 2 lfour-necked flask with magnetic stirrer and dry ice cooling. A bed ofdry molecular sieve 3A (dried for 16 h at 2 mbar/150° C.) is presentover glass wool in both dropping funnels. In one of the droppingfunnels, a layer of 250 g of dry, acidic ion exchanger (Lewatit SPC 118)is placed. over the molecular sieve. Here, a mixture comprising 600 mlof methylene chloride and 600 ml of hexane and cooled to −78° C. ispoured on so that molecular sieve and ion exchanger are flooded and thetotal solvent is present in the reaction flask after 30 minutes. Theother dropping funnel is provided with a dry ice cooler, by means ofwhich 8 mol of isobutene dried at −78° C. over molecular sieve 3A withan average residence time of 15 min are introduced by condensation. Theisobutene feed is effected in the case of the flooded molecular sieve insuch a way that all isobutene is in the flask after 25 minutes.Thereafter, 2 mmol of dry 2,6-di-tert-butylpyridine and 5 mmol ofdicumyl chloride are added by means of a syringe via a septum andcooling to −70° C. is effected by means of dry ice. 60 mmol of TiCl₄ arethen added via the septum with vigorous stirring, no temperatureincrease (polymerization) being detectable under these conditions. After4 hours, a sample is taken and 0.4 mol of styrene is added via theisobutene purification under the same feed conditions as isobutene,after which the reaction mixture is heated to 20° C., the reaction isstopped after 30 min by adding 1 mol of isopropanol, 300 ml of tolueneare added and the mixture is transferred to a separating funnel, washed3 times with 200 ml of water and distilled at 200° C. to 2 mbar. 260 gof polymer are obtained and are dissolved in toluene, poured ontosilicone paper and dried in a drying oven at 140° C. and under a reducedpressure of 30 mbar to give a film.

Before the addition of styrene, a sample of the reaction mixture wastaken and was analyzed with respect to its molecular weight: thenumber-average molecular weight M_(n) was 43,000 dalton and the peakmaximum M_(p) was 44,000 dalton. The molecular weight distributionM_(w)/M_(n) was 1.18.

The solution viscosity of the block copolymer was 1.12 mm²/second.

For the block colpolmer, a glass transition was determined at 95° C. bymenas of DSC.

9. Shore A hardness: 39.2

σmax: 6.5 N/mm² ε-F_(max): 500%

Chlorine content (by elemental analysis): 19 ppm

Permeability to water: 0.35 g/(m²·d)

Permeability to argon: 135 g/(m²·d)

We claim:
 1. A method of sealing a joint by applying a resillientsealing material to the joint, wherein the sealing material consists ofat least one linear or star block copolymer alone or together withcustomary additives for this purpose selected from processingassistants, UV stabilizers and fillers, in a amount of up to 40% byweight, wherein the block copolymer comprises at least one polymer blockA which is essentially composed of isobutene units and at least twopolymer blocks B which are essentially composed of units which arederived from vinylaromatic monomers and conform to the general formula I

where A is a polymer block A, B is a polymer block B. n is 0, 1 or 2 andX is a single bond or an n+2-valent hydrocarbon radial of up to 30carbon atoms, wherein the sum of the number-average molecular weights ofall polymer blocks A is from 30,000 to 80,000 daltons, wherein each ofthe polymer blocks B has a number-average molecular weight M_(n) of from6000 to 20,000 daltons, and wherein the ratio of the total weight of allpolymer blocks A to the total weight of all polymer blocks B is from 3:2to 4:1.
 2. The method as claimed in claim 1, wherein the polymer blocksA contain up to 20% by weight, based on the total weight of all polymerblocks A, of monoolefinically unsaturated monomers having trialkylsilylgroups as polymerized units.
 3. The method as claimed in claim 1,wherein the vinylaromatic monomers are selected from styrene andp-methylstyrene.
 4. The method as claimed in claim 1, wherein X is oneof the following radicals:

where m is 1, 2 or
 3. 5. The method as claimed in claim 1, wherein thejoints to be sealed are the edge joints of insulation glass panes.
 6. Aninsulation glass pane having a flexible edge joint seal which cotains atleast one block copolymer as defined in claim 1.